At present, the expansion of application range of liquid crystal compounds becomes larger and larger, and the liquid crystal compounds can be used in various types of displays, electro-optical devices, sensors and the like. There are a great variety of liquid crystal compounds used in the above-mentioned display field, wherein nematic liquid crystals are used most extensively. Nematic phase liquid crystals have been used in passive TN and STN matrix displays and systems having a TFT active matrix.
With regard to the application field of thin film transistor techniques (TFT-LCD), although the market in recent years has become very huge, and the techniques also become gradually mature, requirements of display techniques are increasing continuously, especially in terms of achieving a quick response, reducing the drive voltage for reducing power consumption, etc. Liquid crystal materials, as one of the important optoelectronic materials for liquid crystal displays, play an important role in improving the performance of a liquid crystal display.
As liquid crystal materials, they need to have good chemical and thermal stability and stability to electric fields and electromagnetic radiations. Moreover, as liquid crystal materials used for thin film transistor techniques (TFT-LCD), they not only need to have the stabilities as mentioned above, but also should have properties, such as a broader nematic phase temperature range, a suitable birefringence anisotropy, a very high electrical resistivity, a good ultraviolet resistant property, a high charge retention rate, a low vapor pressure, etc.
As for dynamic picture display applications, the liquid crystal is required to have a very fast response speed in order to eliminate ghosting and trailing of display pictures, and therefore the liquid crystal is required to have a lower rotary viscosity γ1; in addition, as for portable devices, in order to reduce the energy consumption of equipment, the driving voltage for the liquid crystal is desired to be as low as possible; and as for displays for use in televisions, etc., the requirements for the drive voltage for the liquid crystal are not as low as that.
The viscosity, in particular rotary viscosity γ1, of a liquid crystal compound directly affects the response time after the liquid crystal is energized, and both the rise time (ton) and fall time (toff) are proportional to the rotary viscosity γ1 of the liquid crystal; moreover, since the rise time (ton) is related to a liquid crystal cell and the drive voltage, same can be adjusted by increasing the drive voltage and reducing the thickness of the liquid crystal cell; however, the fall time (toff) is irrelevant to the drive voltage, and is mainly related to the elastic constant of the liquid crystal and the thickness of the liquid crystal cell, and thinning of cell thickness can result in a decrease in the fall time (toff); moreover, the movement manners of liquid crystal molecules in different display modes are different, and the three modes, i.e., TN, IPS and VA, are respectively inversely proportional to the mean elastic constant K, twist elastic constant and bend elastic constant.
According to the continuum theory of liquid crystal, a variety of different liquid crystals deformed under the action of an external force (an electric field, a magnetic field) can “rebound” back to the original shapes by intermolecular interactions; likewise, liquid crystals also form a “viscosity” due to the intermolecular force. Small changes of liquid crystal molecules may result in obvious changes in the conventional parameter performance of the liquid crystal, wherein for some of these changes, there is a certain rule, while for some changes, it is difficult to find a rule, which may also have obvious effects on the intermolecular interaction of the liquid crystal, these effects are very subtle, and to date, no perfect theoretical explanation has been formed yet.
The viscosity of a liquid crystal is related to the molecular structure of the liquid crystal, and studying the relationship between the viscosity of a liquid crystal system formed from different liquid crystal molecules and the molecular structures of the liquid crystals is one of important tasks of liquid crystal formulation engineers.
The reason why a liquid crystal display panel has a high energy consumption is that only about 5% of backlight can transmit through a display device and then be captured by human eyes, while most of the light is “wasted”. If a liquid crystal having a high light transmittance can be developed, then the backlight intensity can be reduced, thereby achieving the purpose of saving energy consumption and extending the service time of a device.
Therefore, there is a need to provide a new liquid crystal display device.